Such a device has been known from West German Offenlegungsschrift No. DE-OS 36,26,728 for the case of catalytic exhaust gas detoxification. The protective ring is consistently round and is held in the housing by means of a holding mat, which also holds the two exhaust gas treatment bodies in the housing. The problem arises here that the protective ring is not always (under all occurring states of operation) held securely against displacement or tilting. In addition, accurate mounting of the holding ring by placing it into a partial shell of the housing and subsequently putting in place and welding the second partial shell is associated at least with a very substantial amount of work.